1. Field of the Invention
The present invention relates to orthopaedic implants, and, more particularly to a method of manufacturing an orthopaedic implant using a post forging process that prevents the covering of surface defects.
2. Description of the Related Art
Orthopaedic implants may be formed using a variety of processes such as milling, casting or forging. It is known to near net forge an orthopaedic implant such that areas of the implant after forging are only slightly larger than the desired finished shape of the implant. Typically, after an implant is near net forged, the implant is exposed to shot peening, grinding or belting techniques to remove scale and excess material. Grinding and belting processes both remove excess material from the implant by abrasive particles which are moved generally parallel to and against the surface of the implant.
Near net forging offers certain advantages in terms of reduced manufacturing costs, predictability and high quality. Moreover, with a near net forging process, very little material must be removed from the implant after forging. This results in decreased manufacturing costs associated with decreased machining. It is, therefore, desirable to use a near net forging process for certain applications of orthopaedic implants.
During the forging process, small surface defects such as cracks or laps may develop in the implant. In a standard forging process, such small surface defects are not critical, as a layer of material containing these cracks or defects will be removed. However, in a near net forging operation, as discussed, only a small amount of material is removed by shot peening, grinding and belting. As these processes are intended only to remove a small layer of material in a near net process, in some circumstances, the crack or defect may not be removed. In fact, a problem with shot peening, grinding and belting is that a portion of the crack at the surface of the implant may be covered or smeared during the machining process. A fragmentary, enlarged cross-sectioned portion of a metallic test specimen having a surface crack covered during a shot peening process is illustrated in FIG. 1. The illustration of FIG. 1 is illustrative of the problems that may be experience when forming an implant using the current technology for removing scale and extra material from a near net forged implant. The implant may be inspected with a fluorescent penetrant to detect the presence of such surface defects. However, if the crack is covered or masked (See FIG. 1) using a shot peening, grinding or belting process, the fluorescent penetrant will not penetrate into the crack such that the crack may be detected. This of course means that when the crack is covered or masked, the implant may have a subsurface discontinuity which is not detected or removed during the manufacturing process.
What is needed in the art is a method of manufacturing an orthopaedic implant using a near net forging technique which allows the implant to be finished without covering or masking the presence of surface defects such as cracks.